In many clinical situations, blood vessels are occluded for a variety of purposes, such as to control bleeding, to prevent blood supply to tumors, to stop blood flow to arterio-venous malformations or fistulas, and to block blood flow within an aneurysm.
Embolization of blood vessels is particularly useful in treating aneurysms. Aneurysms are abnormal blood-filled dilations of a blood vessel wall that may rupture causing significant bleeding. For the cases of intracranial aneurysms, the significant bleeding may lead to damage to surrounding brain tissue or death. Intracranial aneurysms may be difficult to treat when they are formed in remote cerebral blood vessels, which are very difficult to access. If left untreated, hemodynamic forces of normal pulsatile blood flow can rupture fragile tissue in the area of the aneurysm causing a stroke.
Vaso-occlusive devices have been used to treat aneurysms. Vaso-occlusive devices are surgical implants placed within blood vessels or vascular cavities, typically using a catheter, to form a thrombus and occlude the site. For instance, a stroke or other such vascular accident may be treated by placing a vaso-occlusive device proximal of the site to block the flow of blood to the site and alleviate the leakage. An aneurysm may similarly be treated by introducing a vaso-occlusive device through the neck of the aneurysm. The thrombogenic properties of the vaso-occlusive device cause a mass to form in the aneurysm and alleviate the potential for growth of the aneurysm and its subsequent rupture. Other diseases, such as tumors, may often be treated by occluding the blood flow to the tumor.
There are a variety of vaso-occlusive devices suitable for forming thrombi. One such device is found in U.S. Pat. No. 4,994,069, to Ritchart et al., the entirety of which is expressly incorporated by reference herein. That patent describes a vaso-occlusive coil that assumes a linear helical configuration when stretched and a folded convoluted configuration when relaxed. The stretched configuration is used to deliver the coil to the desired site and the convoluted configuration occurs when the coil is ejected from the catheter and the coil relaxes. Ritchart et al. describes a variety of shapes, including “flower” shapes and double vortices. A random shape is described as well.
U.S. Pat. No. 6,280,457B1 to Wallace et al., describes an occlusive device comprising an inner core wire covered with a polymer. The polymeric material includes protein based polymers, absorbable polymers, non-protein based polymers, and combinations thereof. The polymer may contribute to forming emboli for occluding a body cavity.
Vaso-occlusive coils having complex, three-dimensional structures in a relaxed configuration are described in U.S. Pat. No. 6,322,576B1 to Wallace et al. The coils may be deployed in the approximate shape of a sphere, an ovoid, a clover, a box-like structure or other distorted spherical shape. The patent also describes methods of winding the anatomically shaped vaso-occlusive device into appropriately shaped forms and annealing them to form various devices.
Vaso-occlusive coils having little or no inherent secondary shape have also been described. For instance, co-owned U.S. Pat. Nos. 5,690,666 and 5,826,587 by Berenstein et al., describe coils having little or no shape after introduction into the vascular space.
Vaso-occlusive devices work initially by slowing blood flow inside the aneurysm. As a result of the slowed blood flow, the blood inside the aneurysm clots. The combination of the vaso-occlusive devices and the clot protects the aneurysm from hemodynamic forces (i.e., forces on the aneurysm wall due to blood flow) that may cause recanalization and recurrence of the aneurysm. However, recanalization and recurrence of the aneurysm may still occur for various reasons. For example, the vaso-occlusive device may rearrange itself due to the hemodynamic forces. Typically, the vaso-occlusive device(s) near the neck of the aneurysm is most affected by the effects of blood flow. Also, the clot formed may break down due to the hemodynamic forces and/or natural chemical processes. This is more likely to occur if the aneurysm is loosely packed with vaso-occlusive devices.
Accordingly, devices and methods for reducing recanalization or recurrence of an aneurysm would be useful.